1. Field of the Invention
The present invention relates generally to integrated circuits and, more particularly, to thermally-induced signal errors in integrated circuits.
2. Description of the Related Art
An exemplary integrated circuit differential amplifier 20 is shown in FIG. 1. The amplifier 20 has a differential pair 22 of transistors 24 and 25 whose bases are coupled to a differential input port 26 by resistors 28 and 29. Buffers 30 and 31 in the form of emitter-follower transistors couple collectors of the differential pair to an output port 32 and resistors 34 and 35 couple the collectors to a first voltage bias (e.g., ground). An exemplary bias generator in the form of a current source 36 (and its associated current source 37) is coupled between the first bias source and a second bias source (e.g., Vee) and provides a stabilized current which is respectively mirrored by current mirrors 38, 39 and 40 to the differential pair 22 and the buffers 30 and 31.
In its operation, it is intended that the amplifier 20 of FIG. 1 generates an output stream 43 of 50% duty-cycle pulses at the output port 32 in response to an input stream 42 of 50% duty-cycle pulses (for drawing clarity, the input pulse rise times are greatly exagerrated). As also indicated in FIG. 1, it is intended that the amplifier generates an output stream of pulses 45 at the output port whose duty cycle corresponds to that of an input stream 44 of pulses whose duty cycle differs from 50%.
It is often observed, however, that the fidelity of the output pulses degrades as the pulse-stream duty cycle departs from 50%. Examples of this observed signal degradation include:
a) the output duty cycle differs from the input duty cycle,
b) the output stream has an offset voltage and/or a time delay which is a function of duty cycle,
b) the output amplitude varies as a function of duty cycle; and
c) the output amplitude varies over time (i.e., droops or rises in waveforms that are often described as xe2x80x9cthermal tailsxe2x80x9d).
This transfer-function degradation is highly undesirable as it generally produces processing errors in a variety of integrated circuits.
The present invention is directed to reduction of differential-heating signal errors along differential signal paths of electronic circuits.
These goals are realized with a correction sensor that includes first and second transistors which are coupled to different sides of the differential signal path and a differential error amplifier that couples a differential correction signal to the differential signal path in differential response to a differential error signal generated by like terminals of the first and second transistors. In embodiments of the invention, the first and second transistors are directly connected to the different sides.